1. Field of the Invention
The present invention relates to a method of processing an organic film as an interlayer dielectric film formed on a substrate, such as a semiconductor wafer. More specifically, the present invention relates to a method of modifying an organic film formed on a substrate, and coating the modified organic film with a polar liquid or forming an inorganic film on the modified organic film.
2. Description of the Related Art
Reduction of capacitance between wiring lines has progressively become important with the miniaturization of wiring structures to deal with increase in the degree of integration and operation speed of semiconductor devices. Conventional interlayer dielectric films are SiO2 films and SiOF films formed by a CVD process. The SiO2 film has a dielectric constant k in the range of 4.0 to 4.2. Although the dielectric constant k of the SiOF film is smaller than that of the SiO2 film, the dielectric constant k is still in the range of 3.5 to 3.8. A dielectric constant k at such a level is not small enough for a design rule specifying dimensions of 0.18 μm or below, and an interlayer dielectric film having a smaller dielectric constant is needed.
Various low-k materials, i.e., organic film-forming materials having a small dielectric constant, have been developed in recent years. The low-k material is spread over the surface of a substrate in a film by a spin coater, and the film is baked in a baking furnace to form a SOD film having a small dielectric constant as an interlayer dielectric film on the substrate. Since SOD films are organic films and some SOD film is formed in a high porosity to reduce dielectric constant, SOD films have low mechanical strength. Therefore, the SOD film is damaged in some cases when stressed in processing the same by a CMP process or the like. A protective film (hard mask), such as an organic or inorganic film having a necessary mechanical strength, is formed on the low-k film to form a composite film having a small dielectric constant and a necessary mechanical strength.
Thus, the protective film is formed on the low-k film to construct an interlayer dielectric film or the like on a substrate. The low-k film is formed of a hydrophobic material so that the low-k film may not absorb moisture contained in the atmosphere. Therefore, the low-k film repels a hydrophilic chemical liquid applied thereto to form the protective film and, consequently, an irregular film of the hydrophilic chemical liquid is formed. A conventional method of preventing repelling the hydrophilic chemical liquid changes the hydrophobic surface of the low-k film into a hydrophilic surface by oxidization using ultraviolet irradiation or ozonation in order that a film of the chemical liquid having improved uniformity can be formed. A method of improving the adhesion of the protective film to the low-k film forms an intermediate layer on the low-k film.
The conventional method, however, needs an ultraviolet irradiation device or an ozonation device exclusive for changing the hydrophobic surface of the low-k film into a hydrophilic surface. The method using the intermediate layer suffers from the large dielectric constant of the intermediate layer, and needs work for applying a material to the low-k film to form the intermediate layer.
When the low-k film is used instead of the SiO2-series dielectric film, and an inorganic protective film of SiO2, SiN or SiC is deposited on the low-k film by a CVD process or the like, the protective film comes off the low-k film due to difference in molecular structure between the low-k film and the SiO2, SiN or SiC protective film. The surface of the low-k film can be modified by oxidizing the surface by ultraviolet irradiation or ozonation; alkyl groups, such as methyl groups, are removed from the low-k film to make the molecular structure of the low-k film become similar to that of the inorganic protective film. This method, however, needs an ultraviolet irradiation device or an ozonation device exclusive for forming the inorganic protective film.
Various organic film modifying methods using electron beams have been proposed in recent years. For example, a film processing method disclosed in JP2000-221699A improves the quality of an organic film, such as a resist film or an antireflection film, by irradiating the organic film with electron beams in an atmosphere of an oxidizing gas or a reducing gas to promote the carbonization of the organic film. A film quality improving method disclosed in JP11-506872T improves the heat resistance and plasma resistance of an organic film having a small dielectric constant by irradiating the organic film with electron beams in an atmosphere of Oxygen, argon (Ar), nitrogen (N2), helium (He) or a mixture of some of those to cure a dielectric substance. A surface roughening method disclosed in JP2000-053868A cures a resin composition by heating or by irradiation with ultraviolet rays or electron beams.
Those prior art methods disclosed in those references cures the surface of an organic film by promoting the carbonation, oxidation or reduction of the organic film through the irradiation of the organic film with electron beams. Although those prior art methods are able to cure the surface of the organic film by using electron beams, it is difficult to impart wettability to the organic film and to improve the adhesion of the dielectric film to the organic film by those prior art methods. Consequently, it is difficult to form an organic dielectric film having a small dielectric constant and high mechanical strength.
A technique disclosed in JP11-50687T imparts a hydrophilic property to the surface of an organic film by roughening the surface of the organic film after the organic film has been cured. This prior art technique uses a plasma device and does not use electron-beam irradiation devices.